It is known that, in a packet-switched communication network, data are transmitted in the form of packets that are routed from a source node to a destination node through possible intermediate nodes. Each packet typically has a header and a payload. The header generally includes information allowing routing of the packet, such as the source node address and the destination node address. On the other hand, the payload generally comprises a portion of the data to be transmitted from the source node to the destination node. Exemplary packet-switched networks are Local Area Networks (e.g. Ethernet) and Geographic Area Networks (e.g. Internet).
On the other hand, in circuit-switched networks data are transmitted in the form of continuous bit flows carried from the source node to the destination node within plesiochronous or synchronous frames. Exemplary circuit-switched networks are PDH, SDH, Sonet and OTN networks.
Data transmitted either in a packet-switched network or in a circuit-switched network from a source node not always reach the destination node, i.e. they may be lost during transmission through the network. Loss of data may be due to different reasons.
For instance, in a packet-switched network, data within a packet may be discarded by an intermediate node, since the port at which the packet is received or through which the packet has to be forwarded is congested. Indeed, each node is typically suitable for implementing a congestion management algorithm defining rules according to which the node should behave in case one of its ports becomes congested, e.g. due to a traffic peak. More particularly, such a congestion management algorithm typically defines a criterion for selecting the packets to be discarded and the packets to be processed. Such a criterion may be based e.g. on the order according to which the packets arrive at the congested port, their priorities, and so on.
Besides, both in packet-switched networks and in circuit-switched networks, data may be discarded by an intermediate node or by the destination node, since they contain bit errors. Indeed, as it is known, a digital signal transmitted from a first node on a link to a second node may comprise bit errors, i.e. the received digital signal may be different from the transmitted digital signal since a certain number of its bits have wrong values. The parameters of the first node, the second node and the link are typically tailored for achieving a bit error rate lower than a target value, such as e.g. 10−9 (i.e. 1 bit has the wrong value every 1.000.000.000 bits). Data comprising bit errors, if detected, are typically discarded.
For some types of traffic, for which neither the order according to which data are received at the destination node nor the delay between data transmission and data reception is relevant (e.g. non-real time traffic), a mechanism providing re-transmission of discarded data may be implemented. However, for other types of traffic requiring data to be received in a predefined order and with reduced delay, re-transmission of discarded data can not be implemented.
When providing a service by transmitting data through a packet-switched network or a circuit-switched network, the rate of data lost during transmission affects the quality of service (QoS) of that service.
EP 1 879 349 discloses a method of measuring loss of packets in a communications network, comprising the steps of: generating a plurality of packets, each packet having a routing header. The packets are configured to follow a round-trip path in the network. The packets are then sent by a network node and at least a number of the packets are subsequently received at the network node, whereupon the quantity of the at least the number of the packets is evaluated. Together with knowledge of the quantity of packets sent, the quantity of packets received is used to determine a packet loss metric.
U.S. Pat. No. 6,188,674 discloses a method for packet loss measurement by identifying traffic flows in the ingress side of switches, and measuring packets losses for the identifies flows on the egress side of the switches. Specifically, on the ingress side of the switch, the last packet of each fixed size incoming packet block is marked to make it distinct from other packets in the block. On the egress side, the packet flow is monitored and the packets are counted using the block size as a counting modulo. The value of this counter at the receipt of a marked packets is used to update the number of packets that do not make their way across the switch.
WO 2006/102840 discloses a method for monitoring the packet loss rate in the label switched network, including: the message statistics information is carried in the OAM frame for monitoring the packet loss rate and transmitted from the source node of LSP to the destination node; after the destination node receives the OAM frame, it calculates the current packet loss rate based on the message statistics information.